Filter retaining plug

ABSTRACT

A plug for retaining a filter screen in a fluid port of a servovalve, comprises an annular body, the annular body comprising: opposed first and second axial end surfaces, a radially inner surface extending between the first and second axial end surfaces, a radially outer surface extending between the first and second axial end surfaces and at least one recess formed in the radially inner surface for receiving a tool for removing the plug from the port. A tool for removing the plug comprises a pair of handles pivotally mounted to one another about a pivot, each handle having a plug gripping portion extending therefrom beyond the pivot, each plug gripping portion comprising an outwardly projecting tooth for engaging in the recess of the plug when the plug gripping portions are moved apart by operation of the handles.

FOREIGN PRIORITY

This application claims priority to European Patent Application No.18461547.4 filed Apr. 10, 2018, the entire contents of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to plugs which are used to retain afilter in, for example, a servovalve and to tools which may be used inremoving such plugs.

BACKGROUND

Servovalves are used in a wide variety of aircraft control systems, forexample in fuel and air management systems for operating engine fuelmetering valves, active clearance control valves, bleed valves and soon. The operating medium of the servovalve will potentially becontaminated. Accordingly, servovalves are provided with filters. Suchfilters may include filter screens which are assembled in ports of theservovalve, for example in supply, control or return ports of the valve.These screens act to retain any particles which are large enoughpotentially to cause potential failure of the valve. For example in aflapper type servovalve, comprising two nozzles and a movable flapperelement arranged between them, the total flapper operating totaldistance may be as small as about 0.2 mm. In such valves, the filterscreen will typically act to filter out particles having a nominal sizelarger than 0.07 mm. Such filter screens can easily become blocked. Thisnecessitates cleaning or removal and replacement of the filter screens.However, this may be difficult as the filter screen is typicallyretained by a press fitted plug. Removal of this plug is difficult andmay cause damage to the servovalve body, requiring the servovalve itselfthen to require repair.

It would be desirable to provide a system which would mitigate theseproblems.

SUMMARY

From a first aspect, the present disclosure provides a plug forretaining a filter screen in a fluid port of a servovalve. The plugcomprises an annular body. The annular body comprises opposed first andsecond axial end surfaces, a radially inner surface extending betweenthe first and second axial end surfaces, a radially outer surfaceextending between the first and second axial end surfaces, and at leastone recess formed in the radially inner surface for receiving a tool forremoving the plug from the port.

The recess may be an annular recess extending circumferentially aroundthe entire radially inner surface.

The at least one recess may extend perpendicularly to the radially innersurface.

The recess may extend radially into the plug body from the radiallyinner surface to a depth of from 30-50% of the thickness of the plugbody measured between the radially inner and radially outer surfaces ofthe plug body.

The recess may have a height measured in a direction between the firstand second axial end surfaces of 0.25 to 0.43 of the height of the plugbody measured in the direction between the first and second axial endsurfaces.

The plug body may be made from aluminium.

The disclosure also provides a servovalve comprising a port forreceiving a working fluid, a filter screen mounted in the port and aplug in accordance with the disclosure interference fitted in the portto retain the filter screen in the port.

The disclosure also provides a tool for removing a plug in accordancewith the disclosure from a port. The tool comprises a pair of handlespivotally mounted to one another about a pivot, each handle having aplug gripping portion extending therefrom beyond the pivot. Each pluggripping portion comprises an outwardly projecting tooth for engaging inthe recess of the plug when the plug gripping portions are moved apartby operation of the handles.

The plug gripping portions may be configured such that as the handlesare moved towards one another, the plug gripping portions are movedapart.

Each handle may further comprise a stop for limiting the movement of thehandles and therefore the movement apart of the plug gripping portions.

Each stop may comprise an L-shaped element.

Each tooth may taper in an outward direction.

Each handle may comprise a first section arranged generally parallel tothe first section of the other handle and an angled section extendingtherefrom to the pivot.

Each plug gripping portion may comprises a proximal portion attached toa respective handle and a distal portion comprising the outwardlyprojecting tooth, the proximal and distal portions of each plug grippingportion being offset laterally from one another whereby the distalportions of the gripping portions align.

The disclosure also provides a method of maintaining a servovalvecomprising a fluid port and a filter screen retained in the fluid portby a plug in accordance with the disclosure interference fitted withinthe fluid port. The method comprises engaging a removal tool with the atleast one recess of the plug body and pulling the plug out of the portusing the tool. The removal tool may be a tool in accordance with thedisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross-section through a servovalve in accordance with thedisclosure;

FIG. 2 shows an exploded view of the servovalve of FIG. 1;

FIG. 3 shows a cross-sectional view of a plug in accordance with thedisclosure;

FIG. 4 shows a perspective cross-sectional view of the plug of FIG. 3;

FIG. 5 shows a plug removal tool in accordance with the disclosure;

FIG. 6 shows the tool of FIG. 5 in a preliminary stage of removing aplug from a servovalve;

FIG. 7 shows a partial cross-sectional view of the tool in a removalconfiguration engaged with the plug; and

FIG. 8 shows the tool holding the removed plug.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a servovalve 2 comprises a servovalvehousing 4 which houses a pair of nozzles 6 and a flapper element 8. Asis known in the art, the flapper element 8 is deflected in a directionalong the axes of the nozzles 6 by an actuator, not shown, in order tometer a working fluid which passes through the nozzles 6.

The servovalve housing 4 comprises has three ports 10, which allowcommunication of the working fluid to the nozzles 6. The central port 10is typically called a control port and its function is to communicatefluid to an actuator (not shown). This type of servovalve is well knownin the art, being used in a wide variety of aircraft control systems,for example in fuel and air management systems for operating engine fuelmetering valves, active clearance control valves, bleed valves and soon.

Since, as is discussed above, the distances moved by the flapper element8 may be relatively small, in order to prevent operation of the flapperelement 8 being compromised by contamination, particle filters 14 arearranged in one or more of the ports 10. As can be seen in FIG. 1, in anembodiment of the disclosure, the filters 14 are received within a bore16 of the respective ports 10 and are received on an annular shoulder 18at the base of each bore 16.

The filter 14 may be a screen or mesh structure as is known in the art,with an appropriate mesh size. For example, in some embodiments thefilter 14 may be configured to filter particles having a nominal sizelarger than 0.07 mm. The filter 14 may be made from any suitablematerial, for example a metal or a plastics material.

The filter 14 is retained on the shoulder 18 within the bore 16 by aplug 20 which is press fitted into the bore 16. As can be seen in FIGS.3 and 4, the plug 20 has an annular body 22 having opposed first andsecond axial end surfaces 24, 26, a radially inner surface 28 extendingbetween the first and second axial end surfaces 24, 26 and a radiallyouter surface 30 extending between the first and second axial endsurfaces 24. The first and second axial end surfaces 24, 26 aregenerally parallel to one another and perpendicular to the central axisA of the plug 20. The radially inner and outer surfaces 28, 30 are alsogenerally parallel to one another and extend parallel to the centralaxis A of the plug 20.

An annular recess 36 is formed in the radially inner surface 28. In thisembodiment, the recess 36 extends entirely around the circumference ofthe inner surface 28. In other embodiments, however, one or more pairsof diametrically opposed recesses may be provided instead. However, anannular recess 36 may be more easily manufactured and may facilitateremoval of the plug 20.

The recess 36 extends into the plug body 22 generally perpendicularly tothe radially inner surface 28. In the disclosed embodiment, the recess36 has opposed axial surfaces 38, 40 and a base surface 42. The axialsurfaces 38, 40 may, as shown, be parallel to the axial end surfaces 24,26 of the plug body 22. The base surface 42 may be parallel to theradially inner and outer surfaces 28, 30 of the plug body 22.

The recess 36 may extend radially into the plug body 22 from theradially inner surface 28 to a depth D of from 30-50% of the thickness Tof the plug body 22 measured between the radially inner and radiallyouter surfaces 28, 30 of the plug body 22.

The recess 36 may have a height HR measured in the direction between itsopposed axial surfaces 38, 40 of from 0.25 to 0.43 of the height HP ofthe plug body 22 measured between the first and second axial endsurfaces 28, 30 of the plug body 22.

In a typical embodiment, the plug body 22 may have an outer diameter DPOof 7.5 mm and an inner diameter DPI of 4.7 mm and the recess 36 have anouter diameter DR of 6 mm. The inner diameter DPI of the plug body 22will need to be large enough to allow the flow of working fluid throughthe respective ports 10, 12. The height HP of the plug body 22 maytypically be 2.7 mm and the height HR of the recess 36 22 may typicallybe 1 mm.

As can be seen, for example FIG. 3, in embodiments, the plug 20 may besymmetrical about an axial centreline B defined equidistant between thefirst and second axial end surfaces 24, 26 of the plug 20 such that itmay be inserted into the bore 16 in either orientation, therebyfacilitating assembly. Also, as can be seen in FIG. 3, the corners 32,34 between the first and second axial end surfaces 24, 26 and theradially outer surface 30 may be chamfered or rounded in order tofacilitate insertion of the plug 20 into the bore 16.

The plug body 22 may be made from any suitable material. In certainembodiments, the plug body 22 may be made from aluminium for example.This will provide sufficient rigidity and strength for the plug body 22.

As discussed above, the plug body 22 is press fitted into the bore 16 inorder to retain the filter 14 in position. The recess 36 facilitatesremoval of the plug 20 from the bore 16 as will be discussed furtherbelow.

FIG. 5 illustrates a tool 50 which may be used in removing the plug 20from a bore 16.

The tool 50 comprises a pair of handles 52 a, 52 b pivotally mounted toone another about a pivot 54. The pivot 54 may take any suitable form,for example a pin extending through respective openings (not shown) onthe handles 52 a, 52 b. Each handle 52 a, 52 b has a respective pluggripping portion 56 a, 56 b extending therefrom beyond the pivot 54.

Each plug gripping portion 56 a, 56 b comprises an outwardly projectingtooth 58 a, 58 b at its distal end for engaging in the recess 36 of theplug 20 when the plug gripping portions 56 a, 56 b are moved apart byoperation of the handles 52 a, 52 b.

The teeth 58 a, 58 b may have any suitable profile as long as they canbe received within the recess 36. In this embodiment, each tooth 58 a,58 b tapers in an outward direction. Thus, as shown, the upper surface59 of each tooth 58 a, 58 b may be angled. This may facilitatepositioning of the tooth 58 a, 58 b in the recess 36, as can be seenfrom FIG. 7 for example. Of course other shapes of tooth 58 a, 58 b arepossible within the scope of the disclosure

In the disclosed embodiment, the plug gripping portions 56 a, 56 b areconfigured such that as the handles 52 a, 52 b are moved towards oneanother the plug gripping portions 56 a, 56 b are moved apart. Thisfacilitates removal of the plug 20 as it is possible to engage the tool50 with the plug 20 using just one hand.

Each handle 52 a, 52 b further comprises a stop 60 a, 60 b for limitingthe movement of the handles 52 a, 52 b and therefore the movement apartof the plug gripping portions 56 a, 56 b. The stops 60 a, 60 b thereforedetermine how far the teeth 58 a, 58 b will extend into the recess 36and indicate to a user that the teeth 58 a, 58 b are properly located inthe recess 36 when the stops 60 a, 60 b engage.

In the embodiment described, each stop 60 a, 60 b is generally L-shaped,having opposed distal surfaces 62 a, 62 b which will engage with eachother in the closed position. Of course, different forms of stop may beprovided. In this embodiment, both stops 60 a, 60 b extend from arespective handle 52 a, 52 b. In other embodiments, only one stop mayextend from a handle 52 a, 52 b, the other stop being formed as a stopsurface on the handle 52 a, 52 b.

As can be seen from FIG. 5, in this embodiment each handle 52 a, 52 bcomprises a first section 64 a, 64 b arranged generally parallel to thefirst section 64 a, 64 b of the other handle 52 a, 52 b and an angledsection 66 a, 66 b extending therefrom to the pivot 54. The stops 60 a,60 b extend from the angle sections 66 a, 66 b and are cranked such thatthe stop surfaces 62 a, 62 b thereof are generally parallel when theyengage one another.

As can also be seen from FIG. 5, each plug gripping portion 56 a, 56 bcomprises a proximal portion 68 a, 68 b attached to its respectivehandle 52 a, 52 b at the pivot 54 and a distal portion 70 a, 70 bcomprising the outwardly projecting tooth 58 a, 58 b. As the handles 52a, 52 b are spaced laterally along the pivot axis P, the plug grippingportions 56 a, 56 b are shaped such that the proximal portions 68 a, 68b and distal portions 70 a, 70 b are offset laterally from one anotherin the opposite direction so that the distal portions 70 a, 70 b of theplug gripping portions 56 a, 56 b align back to back when the handles 52a, 52 b are spaced apart, thereby assuring that the teeth 58 a, 58 b arealigned. The proximal portions 68 a, 68 b and 70 a, 70 b may therefore,as shown, be joined by an angled section 72 a, 72 b.

Having described the plug 20 and tool 50, removal of a plug 20 from abore 16 will now be described.

Firstly, with the tool 50 in the “closed” position shown in FIG. 5, theplug engaging portions 56 a, 56 b are inserted into the plug 20 as shownin FIG. 6. The tool 50 is inserted to such a depth that the teeth 58 a,58 b lie opposite the recess 36.

The handles 52 a, 52 b are then moved together as indicated by arrow Ain FIG. 6. This will cause the plug gripping portions 56 a, 56 b topivot apart from one another, as shown schematically by the arrow B inFIG. 7. This moves the teeth 58 a, 58 b into the recess 36 as shown inFIG. 7. The movement of the teeth 58 a, 58 b is limited by the stops 60a, 60 b coming into engagement with each other. This will indicate tothe user that the teeth 58 a, 58 b are fully engaged in the recess 36and that the plug 20 may then be removed.

To remove the plug 20, the user pulls on the handles 52 a, 52 b, andpossibly also twists the tool to loosen the plug 20. Once the plug 20has been removed (as shown in FIG. 8) it may be discarded. The filter 14may then be removed, for example using a hook-like tool and the relevantport 10, 12 cleaned if necessary. A new filter 14 may then be placed inthe bore 16 and a new plug 20 press fitted into the bore 16 to retainthe filter 14.

The above described embodiments arrangement offers significantadvantages. Firstly, they may allow easy replacement of a filter 14without the need to return the servovalve 2 to the manufacturer. This isboth attractive in terms of time and cost. The tool 50 also allows easyand consistent gripping of a plug 20 to facilitate its removal. The useof an annular recess 36 is potentially advantageous as it will allow thetool 50 to be engaged in the recess in any angular orientation,facilitating removal of the plug 20.

It will be appreciated that the above embodiments are exemplary only andthat modifications thereto may be made within the scope of thedisclosure.

The invention claimed is:
 1. A plug for retaining a filter screen in afluid port of a servovalve, the plug comprising an annular body, theannular body comprising: opposed first and second axial end surfaces; aradially inner surface extending between the first and second axial endsurfaces; a radially outer surface extending between the first andsecond axial end surfaces; and at least one recess formed in theradially inner surface for receiving a tool for removing the plug fromthe port, wherein the at least one recess is an annular recess extendingaround the entire radially inner surface and having opposed axialsurfaces and a base surface.
 2. A plug as claimed in claim 1, whereinthe at least one recess extends perpendicularly to the radially innersurface.
 3. A plug as claimed in claim 1, wherein the opposed axialsurfaces are parallel to at least one of the first and second axial endsurfaces.
 4. A plug as claimed in claim 1, wherein the base surface isparallel to at least one of the radially inner surface and radiallyouter surface.
 5. A plug as claimed in claim 1, wherein the recessextends radially into the plug body from the radially inner surface to adepth of from 30-50% of the thickness of the plug body measured betweenthe radially inner and radially outer surfaces of the plug body.
 6. Aplug as claimed in claim 1, wherein the recess has a height (H) measuredin a direction between the first and second axial end surfaces of 0.25to 0.43 of the height Hp of the plug body measured in the directionbetween the first and second axial end surfaces.
 7. A plug as claimed inclaim 1, wherein the plug body is made from aluminium.
 8. A servovalvecomprising: a plug as claimed in claim 1, a port for receiving a workingfluid, wherein the filter screen is mounted in a bore of the port andreceived on an annular shoulder at a base of the bore, and wherein theplug is interference fitted in the port to retain the filter screen onthe annular shoulder in the port.